Generally, cars are briefly classified into manual transmission cars and automatic transmission cars. As conductors for electric wires of such cars, mainly annealed copper wires have been used. Recently, as automatic transmission cars become popular, it has been intended to change carburetors into electronic fuel injection systems, and it has been intended to make mobile devices such as various kinds of measuring instruments, etc., be electronic devices. Since the mobile devices are made to be electronic devices, the number of electric and electronic wiring circuits in a car extremely increases, resulting in an increase in the space occupied by electric wires used in the car as well as an increase in weight due to the wires.
It is however desirable that the body of a car is light in weight in the viewpoint of improvement in fuel consumption. The increase in quantity of electric wires to be used is contrary to reduction in weight of the car body. In order to reduce the weight of the car body, it is strongly desired that the electric wires used for electric and electronic wiring circuits in the car are made light and the space occupied by the electric wires is made small.
Of electric wires used in a car, those having extremely fine diameters, such as lead wires, are sufficient for use in a micro-current circuit including, for example, a microcomputer. However, troubles such as separation or disconnection of connection portions of electric wires occurs while the car is running unless the electric wires have sufficient mechanical strength, because extremely large vibratory shocks are caused in running of the car. Conventionally, therefore, conductors having a diameter that is larger than the electrically required value have been used in order to ensure the sufficient mechanical strength.
In the case where electric conductors having a diameter that is larger than the electrically required value are used in order to ensure the sufficient mechanical strength, it is impossible to reduce the weight of the electric wires for use in electric and electronic wiring circuits in a car and to reduce the space occupied by the electric wires.
Hard copper wires capable of ensuring good mechanical strength even if the outer diameter of the electric conductors is made small have been examined in order to reduce the weight of the car electric wires. However, the hard copper wires have extremely low elongation because of the quality of materials thereof. Accordingly, if solderless connection is formed at terminals using the hard copper wires, the connection portions are sometimes damaged when a mechanical load due to external force such as a vibratory shock generated during the car running is applied to the connection portions. That is, if solderless connection is formed at the terminals using the hard copper wires, the terminal solderless contact portions are mechanically weak so that disconnection due to external shocks may be easily caused to thereby make the reliability poor.
Further, although it can be realized to reduce the weight of the car electric wires by making the diameter of their electric conductors small, the mechanical strength is lowered if the diameter of the electric conductors of conventional annealed copper wires is made small. Recently, therefore, a Cu--Ni--Ti alloy, a Cu--Ni--Si alloy and the like, have been proposed as copper alloys that can ensure mechanical strength even if the outer diameter of the electric conductors is small, and which have relatively good repetition bending strength and conductivity.
The Cu--Ni--Ti alloy is disclosed, e.g., in JP-A-60-184655 and JP-A-61-69952 and the Cu--Ni--Si alloy is disclosed, e.g., in JP-A-63-62834, JP-A-63-130752 and JP-A-63-130739. (The term "JP-A" as used herein means an unexamined published Japanese patent application.)
In the Cu--Ni--Ti alloy, the tensile strength is improved without greatly lowering the conductivity by making the Ni--Ti intermetallic compound precipitate into a Cu matrix. However, there is a problem that in the Cu--Ni--Ti alloy, it is still impossible to obtain the tensile strength sufficient to stand against the mechanical load due to the external force such as vibration shocks or the like generated during the car running.
Further, in the Cu--Ni--Si alloy, the tensile strength is improved without lowering the conductivity by making the Ni--Si intermetallic compound precipitate into a Cu matrix. However, there is also a problem that in the Cu--Ni--Si alloy, it is still impossible to obtain the tensile strength sufficient to stand against the mechanical load due to the external force such as vibration shocks or the like generated during the car running.